We have a '96 Dodge Dakota we drive about 400 miles/wk. It's losing water somewhere, have to add water to radiator about every 3 days. Have replaced radiator; etc. no visible sign of leak, still has good power, have done everything we know to do. Mechanic is stumped. Oh yes, only does this is cold weather, say 35 degrees or under. Can go all summer 90+ degree heat and add no water.Has anyone has this problem?

Have you had the vehicle pressure-tested to determine where the leak is? Also check the oil to make sure you don't have a blown head gasket that's leaking internally.